A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network the computing devices communicate data by dividing the data into small blocks called packets. Certain devices within the network, such as routers, maintain routing information that describes routes through the network. In this way, the packets may be individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
A virtual private local area network service (VPLS) may be used to extend two or more remote customer networks, i.e., VPLS sites, through a network (usually referred to as a provider network), such as the Internet, in a transparent manner, i.e., as if the network does not exist. In particular, the VPLS transports layer two (L2) communications, such as Ethernet packets, between customer networks via the network. In a typical configuration, routers coupled to the customer networks (such routers will be referred to as “members of the VPLS”) define label switched paths (LSPs) that may be used as pseudowires within the provider network to carry encapsulated L2 communications as if these customer networks were directly attached to the same local area network (LAN).
Provider edge (PE) routers that are members of the VPLS each maintain state data including all Media Access Control (MAC) addresses learned from locally attached customer sites. In addition, each PE router also maintains state data specifying MAC addresses that belong to remote customer sites that are attached to remote PE routers. The VPLS PE routers learn MAC addresses of remote customer sites over the pseudowires that are established among all the VPLS PE routers. In case of a topology change resulting in teardown of pseudowires, VPLS PE routers delete all MAC addresses that were learned on those pseudowires.